PRISTINA, Jan 16 – Kosovan Serb leader Oliver Ivanovic, who was standing trial over the killings of ethnic Albanians during the 1998-99 war, was shot dead outside his party office in the northern town of Mitrovica on Tuesday, a state prosecutor said.

In a protest against the killing, Serbia said it would quit the ongoing round of a European Union-sponsored dialogue between Belgrade and Pristina on the normalization of relations that was due to take place in Brussels.

President Aleksandar Vucic has called an emergency session of the National Security Council meeting.

“I can confirm that Oliver Ivanovic has died from gun shots. Investigators are on the scene,” Shyqyri Syla, a state prosecutor in Mitrovica, told Reuters.

The European Union condemned the shooting and called on all sides to stay calm, EU foreign policy spokeswoman Maja Kocijancic said.

“We expect the relevant Kosovo Rule of Law authorities to spare no effort to find the perpetrators and bring them to justice without delay,” she said.

Known as a moderate among Kosovo Serb politicians, Ivanovic had been one of the chief interlocutors for NATO, United Nations and European Union officials based in Kosovo after the war.

In 2016 he was found guilty of war crimes linked to the killings of four ethnic Albanians during the war and was jailed for nine years. But after a retrial was ordered he was released last year and allowed to defend himself while free.

The director of Serbia’s government office for Kosovo, Marko juric, said Ivanovic’s killing was “an act of terrorism”.

“This is an attack against the entire Serbian people, a criminal and terorist act that must and will be punished,” Djuric, who was in Brussels attending the talk, told Tanjug news agency.

The Kosovo government also condemned it.

“The killing of Oliver Ivanovic challenges the law and any attempt to establish law and order throughout the entire territory of Kosovo,” the government said in a statement.

Some 40,000-50,000 ethnic Serbs live in northern Kosovo, rejecting integration with the mainly Albanian state since it declared independence from Serbia in 2008.

Relations between Serbia and Kosovo have been tense since 2008, but in 2013 both parties agreed to participate in the EU-sponsored negotiations on normalising relations, a condition for both to progress on their way towards membership in the bloc.

Ivanovic lived in the ethnically divided town of Mitrovica.

The Serbian news agency Tanjug quoted his lawyer as saying he was shot five times.

“He was taken to the hospital immediately, the doctors tried to revive him, but he could not be saved,” lawyer Nebojsa Vlajic said.

Kosovo police said they had found a burned opel car in northern Mitrovica after the shooting and they suspected the car could be linked to shooting.